Technology Roundup: Sludge Treatment

Designed to treat biosolids streams up to one dry ton per hour, the full system employs a twostage process, using pyrolysis in a proprietary rotary drum followed by a post combustion system. The system works in conjunction with a dryer to provide a 10:1 volume or mass reduction of dewatered biosolids. Residual nonvolatile ash is suited for disposal in landfills as a nonhazardous material or filler for road construction, concrete products or similar applications

Dry sludge pellets are fed into the Pyrobustor from a storage container by a screw conveyor. Theyre first pyrolyzed, then oxidized into inert ash. At just 810% of original weight (compared to mechanically dewatered sludge), the ash is used as filler at a nearby brickproduction facility. The energy side of this technical approach is net positive. Liberated heat of combustion from the sludge is used first to heat the thermal oil for heating the sewage sludge drier, then to heat process water for preheating the air of the drier. This concept yields savings of up to 65% compared to primary energy previously needed for the drying process. In 2008, plant operators replaced the outdated dryer/pelletizer system with a new convection belt dryer system further improving the operations overall energy balance and performance.

Announcing introduction of its Pyrobustor? thermal biosolids treatment system to the U.S. market and creation of a business unit in Crystal Lake, Illinois, near Chicago, Eisenmann Service GmbH released a case study on its first installation in the Pustertal valley in South Tyrol, Italy. The regional treatment plant was constructed in 1996 inside Tobl Mountain to treat residential wastewater from an association of then 14 municipalities in a collection area of 444 square miles. Installed and optimized in 2005, the thermal treatment system has been in continuous operation since early 2006. It converts dry sludge pellets with a calorific value of up to 5,160 BTU/lb and 1020% residual moisture into ash in a continuous process sized for a throughput of 1,200 lb/h with 7,500 hours of operation per year. Fully automatic operations are controlled by a PLC system and monitored via PC plant visualization.